1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to an improved secondary battery having a simple structure.
2. Description of the Related Art
A secondary battery can be classified into two types according to its use and capacity: a battery with a small capacity (hereinafter, referred to as a small-sized battery consisting of one or several cells; and a battery with a large capacity (hereinafter, referred to as a large-sized battery) consisting of tens of cells.
Of these, a small-sized battery is used as a power source for compact electronic equipment, such as a cellular phone, a laptop computer, a camcorder, and so on, and a large-sized battery is used as a power source for a motor, such as a motor of a hybrid electric vehicle.
When a small-sized battery is composed of only one cell, it usually has a cylindrical or hexahedral shape, and is fabricated by interposing a separator as an insulator between band-shaped positive and negative electrodes, and then winding them together to form a spiral-shaped electrode assembly (as a jelly-roll configuration), and inserting the assembly into a cylindrical case.
Then, each lead terminal, i.e. a conductive tab electrically connected to each electrode of the battery, is respectively affixed to the positive and negative electrodes by welding.
However, the structure of a small-sized battery as fabricated above can not be directly applied to a large-sized battery because it does not satisfy the working properties of a large-sized battery in terms of capacity and output and needs to be improved in various ways to be fit for them.
There occurs another problem, that is, modifying the design of a small-sized battery to be fit for the working properties of a large-sized battery raises the manufacturing cost as its internal design becomes more complicated, thereby requiring more fabricating procedures and labor. For example, a case containing an electrode assembly is one of the main factors raising the production cost of a large-sized battery, because a case is usually made by using a die requiring high manufacturing cost.
Furthermore, a large-sized battery requires a particular structure to easily connect the battery cells, unlike a small-sized battery, because a large-sized battery uses tens of secondary battery cells. It also requires a high current collection efficiency to satisfy its working properties, such as a high output. Therefore, another factor in designing a successful large-sized battery depends on the connection between the electrode assembly and electrode terminals.